The invention relates to a pump arrangement, in particular magnetic clutch pump arrangement. The pump arrangement has an interior space formed by a pump casing of the pump arrangement, a containment can which hermetically seals off a chamber surrounded by said containment can with respect to the interior space formed by the pump casing, an impeller shaft which can be driven in rotation about an axis of rotation, an impeller which is arranged on one end of the impeller shaft, an inner rotor arranged on the other end of the impeller shaft, having a drive motor, a drive shaft which can be driven rotatably about the axis of rotation by the drive motor, and an outer rotor which is arranged on the drive shaft and which interacts with the inner rotor, wherein the outer rotor has a hub and a first carrier element.
Pump arrangements of said type are widely used and can be found in almost all sectors of industry. Machines of the present type are also used in explosive environments. For different production and conveying installations, in particular in the chemical sector, there are particular guidelines relating to explosion protection. In such installations, use is made, on the one hand, of working machines, for example pumps or turbines, as non-electrical devices, and on the other hand, of power machines, for example drive motors, as electrical devices. Proven safety standards have existed for a long time for electrical devices. Said standards specify the structural measures that must be implemented in order that an electrical device can be used in the various explosive environments. In areas in which the generation of an explosive atmosphere is possible, ignition sources, that is to say the generation of sparks as a result of friction or impact, friction heat and electrical charging, must be avoided, and possible effects of an explosion must be allowed for by way of preventative and structural measures. Explosion-protected block motors, in particular standard motors of flange-type design, permit only a certain introduction of heat into the motor at the interfaces, in particular flange and shaft, such that the maximum admissible temperatures of the motor are not exceeded.
It has lately become known, in the case of magnetic clutch pump arrangements, that the main introduction of heat into the drive motor takes place through the drive shaft thereof, as the outer magnet carrier of the magnetic clutch is exposed both to the temperature of the media and also to the temperature increase resulting from eddy current losses. The poor heat dissipation from the outer magnet carrier owing to the likewise heated pump casing has the effect that the heat energy is introduced predominantly directly into the drive shaft.
In German patent document no. DE 298 14 113 U1, said problem is circumvented by virtue of the outer rotor, referred to as driver, and the drive motor being connected by way of a drive means composed of a material with low thermal conductivity. A disadvantage here is the expensive embodiment with an interposed outer rotor. This is because, aside from the requirement for additional components, not only the motor rolling bearing but also the deep-groove ball bearings which serve for the mounting of the outer rotor have to be serviced. Furthermore, the heat barrier function exists only at the interface to the motor shaft stub. However, since the heat is introduced directly into the inner ring of the deep-groove ball bearings, expansion of the inner ring and thus bracing of the bearing occur, consequently resulting in a reduction in service life. In the case of an embodiment which acts with coolant, the outer rotor runs in the coolant, giving rise to considerable friction losses, which considerably reduce the efficiency of the pump.
It is the object of the invention to provide a pump arrangement which, in the case of an increased temperature of the medium to be delivered, while simultaneously maintaining the explosion protection of the drive motor, permits a reduction in axial and radial structural space and a simplification of the assembly process.
The object on which the invention is based is achieved in that the outer rotor has a hollow cylindrical section between the hub and the first carrier element.
By virtue of the fact that the hub is arranged not directly on the first carrier element but is connected via the hollow cylindrical section to the drive shaft, the introduction of heat from the outer magnet carrier into the drive shaft, and thus into the drive motor, is reduced.
In one refinement of the invention, the hollow cylindrical section and the hub are of thin-walled form in relation to the first carrier element. The hollow cylindrical section and the hub each have a wall with a certain wall thickness, wherein the wall thickness of the wall of the hollow cylindrical section and the wall thickness of the wall of the hub are smaller than the radius of the drive shaft, and are selected such that, in all situations, reliable torsional and bending fatigue strength is ensured. This leads to a further reduction of the introduction of heat from the outer magnet carrier into the drive shaft of the drive motor.
One advantageous refinement provides that the axial fixing of the outer magnet carrier to the drive shaft is realized by way of a fastening element.
Here, ideally, the fastening element has a first external thread on one end and has a second external thread on the end situated opposite the first external thread, wherein, between the first external thread and the second external thread, there is situated a spacer section, the outer diameter of which is greater than the outer diameter of the first external thread and of the second external thread.
What has proven to be particularly advantageous is a refinement in which the spacer section has, on the side close to the first external thread, a collar of increased outer diameter, whereby the fastening element can be positioned axially in an exact manner and fastened in uncomplicated fashion.
Alternatively, the spacer section may taper off conically at the side close to the first external thread.
It is expediently provided that, in the hub, there is formed a radial threaded bore into which a screw element is screwed. Thus, when the pump arrangement is at a standstill, the hub abuts against the drive shaft at the point which is abutted against by the hub during operation. A high level of true running accuracy is achieved in this way.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.